sending with user_ref

[eranartzi]

Hi, I wanted to know if there's a way to send a message from a page with a user_ref and not with an id?
When receiving data for a user from the FB Messenger Checkbox plugin I receive a user_ref and need to pass it on to the send method with the appropriate key. as specified here under item 6:
https://developers.facebook.com/docs/messenger-platform/discovery/checkbox-plugin/